Abstract:

We analyzed the total organic carbon (TOC), total nitrogen (TN), bulk organic matter δ13C, and δ15N as well as magnetic
index s-ratio in the sediment of Huguangyan Maar Lake in order to reconstruct the lake paleo-productivity and paleo-environmental
changes through the Holocene. We divide the Holocene into three stages. The early Holocene (10400~6100 yr BP) is characterized by
high TOC, high TN, high δ13CTOC and low δ15N as well as low s-ratio, reflecting a high primary productivity and a warm and wet climate;
The lowest values of δ15N coupled with high TN during 8500 to 7100 yr BP might be attributed to the expansion of nitrogen-fixation
cyanobacteria. During the mid-Holocene (6100~3600 yr BP), TOC, TN and δ13CTOC decreased while δ15N and s-ratio increased,
suggesting a decreasing primary productivity and a cooler and drier climate. The late Holocene (3600 yr BP to present) is the coolest
and driest period of the Holocene, indicated by the constantly low TOC, TN and saturated s-ratio (~1). Such trend indicates gradually
weakened summer monsoon driven by decreasing summer solar radiation at 30°N through the Holocene. The δ13CTOC was low and δ15N
was high before 1000 yr BP. However, their variations after 1000 yr BP are not consistent with the Holocene climate trend, and are
probably a result of anthropogenic activity.

Key words: Huguangyan maar Lake, Holocene, total nitrogen, bulk organic carbon isotope, nitrogen isotope